1. Field of the Invention
The present invention relates to an object detecting device for detecting an object by transmitting an electromagnetic wave comprising a laser or a millimeter wave to the object and receiving a reflected wave thereof.
2. Description of the Related Art
There is an object detecting device already proposed by the present assignee (see Japanese Patent Application No. 10-200035), which is designed to detect distances to targets T.sub.1, T.sub.2 - - - and their lateral positions (vehicles traveling ahead of a vehicle) by vertically and laterally scanning with an electromagnetic wave transmitted forwards from a radar system mounted at a front portion of a vehicle V, and receiving a wave reflected by the targets T.sub.1, T.sub.2 - - -, which device is included in the arrangement of FIG. 6 showing an embodiment of the invention. In this object detecting device, the space for carrying out the detection of the targets T.sub.1, T.sub.2 - - - is divided into a plurality of detection areas K1 to K15 having a width substantially equal to the lateral width of the vehicle V. Each of the detection areas K1 to K15 is divided into measure-shaped regions depending on the distance from the vehicle V by distance addresses [1] to [200], so that the distances to the targets T.sub.1, T.sub.2 - - - and their lateral positions are detected based on a value resulting from the addition of signals indicative of reception levels of reflected waves in the measure-shaped regions.
In the above object detecting device, when reflectors R.sub.2, R.sub.2 are not mounted on rear surfaces of the targets T.sub.1, T.sub.2 - - -, the detected lateral widths of the targets T.sub.1, T.sub.2 - - - are equal to the actual lateral widths of the targets T.sub.1, T.sub.2 - - -. However, when highly reflective reflectors R.sub.2, R.sub.2 are mounted on the rear surfaces of the targets T.sub.1, T.sub.2 - - -, signals indicative of reception levels of the reflected waves in a region in which the reflectors R.sub.2, R.sub.2 are included, are increased, and also signals indicative of reception levels of the reflected waves in a region around the reflectors R.sub.2, R.sub.2 are increased. Therefore, there is a possibility that the lateral widths of the targets T.sub.1, T.sub.2 - - - may be detected as values larger than the actual lateral widths of the targets T.sub.1, T.sub.2 - - -.
When a plurality of targets T.sub.1, T.sub.2 - - - having highly reflective reflectors R.sub.2, R.sub.2 exist laterally adjacent one another at the same distance, or when highly reflective reflectors R.sub.1 are mounted on a road and the reflectors R.sub.1 and targets T.sub.1, T.sub.2 - - - exist laterally adjacent one another at the same distance, there is a possibility that the targets T.sub.1, T.sub.2 - - - may be merged together, or the targets T.sub.1, T.sub.2 - - - and the reflectors R.sub.1 on the road may be merged with each other, so that they may be detected as one target T.sub.1, T.sub.2 having a large lateral width.